Fenris Creations, the developer behind EVE Online and EVE Frontier, has unveiled CORTAO, a new open-source rendering technique designed to improve shading accuracy, visual depth and performance efficiency in video games. Announced on November 12, 2026, the technology is available to developers through a public reference implementation and the company’s Carbon game engine framework.
CORTAO, short for Circular Occluder Ray-Traced Ambient Occlusion, was created by Daniel Isheden, Senior Rendering Engineer at Fenris Creations. The technique uses an alternative approach to screen-space ambient occlusion (SSAO), aiming to produce more accurate and stable lighting effects without the processing costs typically associated with full hardware ray tracing.
Ambient occlusion simulates the subtle darkening that occurs when surrounding objects obstruct environmental light. These effects help establish visual depth, particularly around corners, overlapping surfaces and objects resting against one another.
Traditional screen-space techniques estimate this shading using information already rendered on the screen. Although efficient, they can introduce dark halos, inaccurate shadows and noticeable changes in shading as the camera moves.
CORTAO attempts to address these limitations through a different method of calculating occlusion.
Unlike established approaches such as Ground Truth Ambient Occlusion (GTAO), which estimate obstruction using horizon angles, CORTAO constructs simplified circular representations of nearby surfaces from the scene’s depth information.
It then traces rays against this approximated geometry to determine how much ambient light reaches individual pixels.
According to the project’s technical documentation, CORTAO can evaluate up to 32 rays per pixel using precomputed lookup tables to reduce the computational expense. This allows the technique to approximate ray-traced ambient occlusion while remaining suitable for real-time rendering.
The approach is particularly relevant to sloped surfaces and depth discontinuities, where conventional horizon-based methods can overestimate occlusion or produce inaccurate shading.
CORTAO also calculates bent normals, which represent the average direction from which unobstructed ambient light can reach a surface. This information can help rendering engines produce more consistent indirect lighting effects.
Fenris Creations says the technique delivers improvements in both image accuracy and rendering efficiency compared with GTAO.
In benchmark comparisons published with the reference implementation, the developer reports that CORTAO achieves similar accuracy to GTAO in less than half the GPU processing time in simple scenes. At equivalent GPU time budgets, its average squared error was reportedly up to four times lower.
The developer also reports larger accuracy advantages in geometrically complex scenes containing numerous depth discontinuities.
These figures come from the project’s own testing and have not been independently verified across different GPUs, game engines or commercial titles. They should not be interpreted as guaranteed frame-rate improvements for players.
Another claimed advantage is greater consistency across graphics quality settings. According to the documentation, CORTAO can reduce the number of samples while maintaining a more consistent overall appearance, potentially allowing developers to adjust rendering costs without substantially changing the visual character of a scene.
The implementation includes an optional spatial filtering stage intended to work alongside temporal filtering systems. CORTAO does not provide its own complete temporal filtering solution, so developers must integrate an appropriate external method to reduce noise across frames.
Fenris Creations has already optimized and tested the technology within EVE Frontier, its in-development space survival MMO.
The game’s enormous space environments, large structures and player-created installations provide a testing environment for ambient occlusion across dramatically different scales.
Unlike lighting techniques that depend on previously calculated scene information, CORTAO calculates its effects in real time. Fenris Creations says this makes it particularly suitable for game worlds where players can continually construct, modify and rearrange objects.
The company has also released an in-engine EVE Frontier demonstration showing how CORTAO affects visual depth and object shading.
CORTAO originated as Isheden’s independent research before Fenris Creations provided the development environment needed to refine and test the technique in a production engine.
The public release includes an MIT-licensed reference implementation alongside a Carbon-specific version adapted for the extensive depth ranges encountered in space environments.
According to the repository documentation, the reference shaders support HLSL and GLSL and have been tested with DirectX 11, DirectX 12, OpenGL 4.3 and newer, and Vulkan 1.0 and newer. DirectX 11 integration requires a documented workaround for Shader Model compatibility.
CORTAO is designed to replace an existing screen-space ambient occlusion stage rather than require an entirely new graphics pipeline, although integration and performance will depend on the engine.
Its release expands the publicly available rendering technology within Carbon, the framework used by EVE Online and EVE Frontier.
For game developers, the significance is the availability of an adaptable ambient occlusion technique with documented implementation details and performance comparisons. For players, any resulting visual improvements will depend on whether developers adopt CORTAO and how they configure it in their games.
The announcement also arrives as graphics developers continue exploring more efficient rendering methods, including NVIDIA DLSS 5's neural rendering technology. Unlike upscaling and neural rendering systems, CORTAO specifically targets the calculation of ambient occlusion.
Fenris Creations has made both the reference implementation and the Carbon-optimized version publicly available, allowing other studios to evaluate the technique and potentially integrate it into their own rendering pipelines.
